AB0706 Demographic, clinical and serological characteristics in Idiopathic Inflammatory Myopathies. The role of specific antibodies
Authors: X. E. Larco Rojas, S. Sáez-Álvarez, P. Pérez-García, C. Sieiro Santos, I. González Fernández, C. Moriano, A. López Robles, M. Martín Martín, C. Álvarez Castro, E. Diez Alvarez
Journal: Annals of the Rheumatic Diseases (2022)

Background Idiopathic Inflammatory myopathies are a heterogenous group of diseases which main common characteristic is muscle injury. Specific autoantibodies related with different phenotypes have become an important diagnostic and prognostic tool. These antibodies may be associated with different histopathological features in muscle biopsies. Objectives To describe the demographic, clinical and serological characteristics of Idiopathic Inflammatory Myopathies (IIM); the most frequent corticoid sparing agents used and the frequency of associated neoplasms in a sample of patients with a compatible biopsy result. To compare these characteristics in patients with positive and negative ANA and the association of different biopsy patterns with specific myositis antibodies. Methods Muscle biopsies results that were compatible with inflammatory myopathy were collected from the Pathology Unit database of Leon´s hospital between January 2010 and March 2021.Demographic, clinical and serological characteristics, associated malignancies and treatments used were collected from clinical records. Results We included 30 patients in the study. Patient`s characteristics are shown in Table 1. Median age of diagnosis was 59 years. Arthritis and lung disease were found in 20% of patients. The patterns of lung involvement found in HRCT were NSIP in 2, UIP in 1, and bronchiectasis in 3 patients. Associated collagenopathies were found in 26,7%, being vasculitis the most frequent (2 patients). Associated Malignancies were found in 13,3%: lung carcinoma in 1, Urothelial carcinoma in 1, cervix carcinoma in 1 and prostate carcinoma 1 patient. Specific myositis antibodies were negative in 56,7%; positive ANA was found in 60%. Table 1. Demographic, clinical, serological characteristics and treatment in the sample studied Characteristics Patients (n=30)Median; IQR or n(%) Age at diagnosis (years) 59; 18,5 Sex F/M 17(56,7)/13(43,3) Artralgias 11(36,7) Arthritis 6(20) Raynaud 3(10) Lung disease 6 (20) Skin disease 7 (23,3) Autoimmunity biomarkers (+/-/ not done) ACPA 2(6,7) /3 (10) /25(83,3) Positive Rheumatoid Factor 4(13,3) /13 (43,3) /13(43,3) ANA 18 (60%) /12(40%) Specific Myositis Antibodies Anti SRP 1(3,3) Anti-HMG CoA reductase 5 (16,7) Anti Jo1 2(6,7) Negative 17 (56,7) Not done 5 (16,4) Biopsy pattern necrotizing 8 (26,7) inflammatory 15(50) Inclusion Bodies 4 (13,3) dermatomyositis 3 (10) Diagnosis Dermatomyositis 3 (10) Statin Myopathy 5(16,7) Inclusion body myopathy 3(10) Polymyositis 8(26,7) Immune-mediated necrotizing myopathy 2 (6,7) Antisynthetase syndrome 1(3,3) Other collagenopathies 8(26,7) Treatment Methotrexate 11(36,7) Azathioprine 3(10) immunoglobulins 5(16,7) Rituximab 5(16,7) Mycophenolate 4(13,3) Cyclophosphamide 2 (6,7) None 11 (36,7) 2 or more treatments 8(26,7) Associated malignancies 4 (13,3) The median of levels at diagnosis of CK was: 1181; IQR:6252,5; aldolase 14,4; IQR: 34,65; AST 62; IQR:181,25; ALT 55,5; IQR:119,25; CRP 7,6; IQR 13,55. When compared, CK and ALT levels in patients with negative and positive ANA, this were higher in negative patients (6365; IQR:9592vs888;3045; P=0.044) and (182; IQR:287vs43; 85; P=0,035) respectively. Anti HMGCoA reductase antibodies were more frequently found in patients with necrotizing pattern in biopsies 5/8 patients; (62,5%); p=0.002. Methotrexate was the corticoid sparing agent most frequently used (36,7% of patients), 36,7% of patients were treated only with corticoids and 26,7% needed more than one treatment. Conclusion Specific myositis antibodies are helpful tools in the diagnosis when present, meanwhile biopsy can be an important tool when antibodies are negative. ANA positivity seems to be associated with milder disease at the muscular domain. References [1]Zanframundo G,Tripoli A, Cometi L, et al. One year in review 2020: idiopathic inflammatory myopathies. Clin Exp Rheumatol 2021; 39: 1-12. Disclosure of Interests None declared